Steel with lead and rare earth metals



p 1967 D. CORRADINI 3,313,2@

STEEL WITH LEAD AND RARE EARTH METALS Filed Feb. 12, 1964 wan DANTE C RRA P United States Patent 3,313,620 STEEL WITH LEA!) AN!) RARE EARTH METALS Dante Corradini, listoia, ltaly, assignor to E.I.TE.R. S.p.A. Elettrochirnica Italiana delle Terre Rare, Florence, ltaly, an Italian corporate body Filed Feb. 12, 1964, Ser. No. 344,261 Claims priority, application Italy, Feb. 18, 1963, 3,630/63 Claims. (Cl. 75-123) The present invention provides a new method of manufacturing free machining steels, through introduction of new lead compounds or alloys or mixtures; the invention also relates to free machining lead steels containing rare earth elements and other materials mentioned herein.

The difficulties of introduction of lead into liquid steel are known and also the necessity for homogeneous dispersion of the same lead in the steel matrix is well known.

Several processes have been contemplated; ranging from the introduction of meta lic lead in the form of pieces or balls to the introduction of binary alloys Pb-AS, Pb-Cd, Pb-Te, Pb-Na, Pb-Sn, or using the mineral galena (PbS). In this last case, in addition to lead, there is high sulphur contents in the steel. Sulphur, phosphor, and nitrogen impair the properties of these steels and prejudice heat treatment and hot working. The presence of a large quantity of iron sulphides in steel greatly reduces the mechanical properties and the tensile strength is lowered to such an extent that these steels cannot be subjected to heavy mechanical stresses. The presence of sulphur in the steel is attempted to be maintained at the minimum, and i.e. at content lower than 0.02 percent.

Additions of lead in the steel in the metallic state or alloyed with the above mentioned elements or with galena (PbS) are produced for the unique purpose of increasing the speeds allowed for the mechanical working or machining of the steel itself, trying not to prejudiceas it often occurs-the other mechanical properties of the steels. These properties will be impaired as more oxides and metalloids are present in the steel, when compared with the degree of distribution of the lead in the matrix of the steel itself.

It has now been found--according to the invention that by adding metals of the lanthanides (rare earths) group, hereinafter indicated by RE, (misch metal rare metals=RE) either in a single manner or accumulatively, the introduction and distribution of lead in the steel is highly facilitated with respect to the systems known today, and moreover that the presence of rare earths in steels improves their mechanical properties.

The accompanying drawing is a longitudinal sectional view of an ingot divided into four pieces by three horizontal cuts, each piece being subsequently formed into a rod or coil for which test data is given below.

It is the object of the invention to provide a process for the manufacture of lead steels, that is free machining steels, consisting in the introduction of one or more metals of rare earth group into steels in the liquid state, as homogeneizing and dispersing agents of the lead in the steel matrix, thus improving the quality of final products.

Through this system, that is, by using Pb-RE alloys or compounds or sinterized aggregates of these elements, the lead is homogeneously dispersed or scattered in the interdendritic spaces and the mechanical and technological properties of the resulting steels are improved.

Another object of the invention is to produce a lead steel which includes one or more metals of the rare earth group, and creates a more homogeneous dispersion of the lead in the steel and improves the properties of the final product.

Still another object of the invention is to provide a lead alloy with one or more rare earth metals, or a corresponding sinterized aggregate or sinter, said alloy or sinter being designed to be introduced into the steel for production of lead steels having the above defined particular properties.

Metals of the rare earths are intended those of the lanthanides group, which are those include-d from No. 58 to No. 72 of the Mendelieif Periodic System. It is preferred to use metals (hereinafter referred to as misch metal) produced from chlorides by electrolysis which may be used in any proportion.

It is already known that additions of the metals of the rare earth group impart to the steels treated in this manner particular properties of strength, ductility, impact or resilience, etc. due to the fact that these metals, owing to their physical-chemical properties, are strong deoxidizers, desulphun'zers, dehydrogenizers and denitrogenizes, forming stable compounds at the melting temperature of the steel of the type RE Og-REH-RE s -REN.

It can be stated that it is possible to obtain free machining steel by adding lead simultaneously-in the form of an alloy or a sinterized compound or sinterwith the rare earths metals (especially the so-called misch metal produced from chlorides by electrolysis or by other reduction processes), which metals remarkably increase the mechanical properties of the steel, while they do not alter the specific properties conferred heretofore by lead, and contribute to the fine dispersion of lead in the interdendritic spaces, not having, therefore, any abnormal concentrations of lead through the grains and in the matrix of the steel.

Standard production practices used in the manufacture of steels can be followed up to the moment of the introduction of Pb-RE alloys or sinters. The addition may be made with total combined Pb-RE percentages from 0.10% to 0.80% with respect to the steel.

Differing from the case of the use of galena and some other lead base alloys, there are no restrictions in the use of the Pb-RE alloy or sinter, which may be added to all types of steel, including carbon steel, low and high alloy steels and stainless steels.

The Pb-RE alloy may be added in the form of ingots, splits, balls or small pieces of other shapes, or in powdered form. The addition may be effected in furnace, ladles or ingot moulds. The same applies for sinter material. The addition in ingot moulds will allow the use of smaller percentages of Pb-RE alloy or sinteral material to obtain the desired effects; in fact this type of addition reduces the loss from evaporation and oxidation. In any case, disadvantages due to the introduction of lead added alone are avoided.

The simultaneous addition of Pb-RE alloy or of the same elements in the form of a sinterized product, produces a free cutting steel which can be quickly and easily machined, due to the finely dispersed particles of lead, maintaining and in many cases increasing the mechanical properties of the treated steels, in relation to their composition, with respect to the other standard lead steels. The aforesaid addition also allows one to obtain a uniform dispersion of the lead in the steel throughout the length of the ingot without appreciable percent variations in the ends and central portion of an ingot after it has solidified; diminishing the unsatisfactory material in the extremities of the ingot where generally is found the largest concentration of lead. Finally, the production of lead vapors, which are extremely dangerous, is greatly diminished.

According to the invention a Pb-RE alloy or sinterized compounds of the same elements, are produced, wherein RE serves as a vehicle for introduction of lead and as .an homogeneizer of the lead particles in the steel, de-

creasing or even eliminating the coagulation and exudations and conferring also simultaneouslywith the reduction an elimination of the metalloids contained in the steelthose intrinsic mechanical properties which are known and for which RE additions are already used.

The manufacture of the lead-misch metal, although presenting some metallurgical difficulties, can be made with controlled atmosphere furnaces (especially in nitrogen and argon), or with other particular crucible furnaces, using some protection salts, provided the conditions of not letting the misch metal oxidize, during the group, Ce, La, Ne, Pr and others. In the present case,

and without incurring any disadvantage, it is possible to make a complex alloy using the misch metal and lead, introducing the former into the latter and preferably working on the compound RE-Pb In the case of the sinter, the above stated factors still serve as a base, but they may vary in relation to the particular structures of the sinter, and to the possibility of forming some compounds out of the solid solutions,

- typical of the alloys.

It is possible to make some alloys, or sinters of RE in the lead, in the order from 2% to 30%; for alloys designed for the introduction of the lead into the steels and simultaneously for the addition of RE to the latter.

Preference is for alloys in which the percentage ofrare earths included is in the range from 5 to 25% with respect to the weight of the alloy or the sinter.

The percentages of use of the Pb-RE alloy or sinter in weight of steel vary with the contents of Pb and RE which is desired to be added.

Example: the alloy or sinter 80% Pb-% RE added in the percentage of 1% with respect to the steel, will introduce approximately 0.08% Pb and 0.02% RE.

The alloys or sintered aggregates containing RE percentages smaller than those of the example (such as 5- 10-15%), also those with percentages higher than those shown in the example (such as 30%), serve when it is desired to introduce into the steel, higher or smaller percentages of lead respectively, maintaining unaltered the addition of RE unchanged and thus having only the task of facilitating the introduction of higher or lower percentages of Pb into the steel.

The best machining properties of the present steel are obtained with Pb contents from 0.10% to 0.35% in relation to the steel, but it is also possible to add up to 0.80% The best results of the RE additions are obtained with additions ranging from 0.02% to 0.08% in relation to the steel; but depending upon the composition of the steel and of its purity, these contents may vary from 0.02% to 0.30% in relation to the steel.

Hereinafter the results of carbon steel having the following composition:

C 0.075 Mn 0.39 Si 0.20 P 0.014 S 0.028 Pb 0.23

This carbon steel was treated with a Pb-RE type alloy with 80% Pb and 20% RE. The addition was effected in the ladle with 0.33% alloy, equal to kilos 3.300 per 4 metric ton of steel, and thus with 0.264% of Pb and 0.066% of RE.

Microscopic tests have been made both at the riser and at the foot, that is, at the upper end and lower end of the ingot sections, and also after each rolling of the sections, encountering in all stages a material free of any defect. The section was examined and the lead was found to be uniformly distributed throughout the entire length of the portions of the ingot with values varying from 0.23% in the top to 0.24% in the bottom. The sections of the ingot were rolled down to rods having a 6 mm. diameter without any disadvantages. The mechanical properties of the coil are illustrated in the following Table I. In Table I the yield strength (S) is given in kilos/sq. mm; tensile strength (R) in kilos/ sq. mm.; percentage elongation (A%); percentage reduced-area (C% are shown in the different columns. Four pieces were machined (see drawing) by dividing an ingot into four pieces by three horizontal cuts X, Y, Z; said pieces being numbered by l, 2, 3, 4 from top to bottom; the initial or top portions of the material of each piece being respectively indicated by P P P P and the bottom portions of each piece being indicated by C C C 0., respectively; the data shown refers to the materials of the top and bottom portions of each coil, numbered as mentioned above.

The structure was comparable to a low carbon steel having a uniform grain of K2 size.

Subsequently the coils of 6 mm. diameter were drawn to a 5 mm. diameter and the mechanical characteristics resulted as follows in Table II, in which the symbols have the same meaning as those of Table I except for the elongation A% 5d.

TABLE II Strength, mm.

Elonga- Reducedtion, Pct. Area, Pet. #1 mm. Yield (S) Tensile (A 5d) (C) Coil 1 5 59. 8 63. 5 13 58 Coil 2 5 65 67. 5 10 56 Coil 3 5 6G 69. 5 10 56 Coil 4 5 66 69 10 56 Other tests have been made similar to the above ex ample with the results coinciding with the above findings and the invention is not restricted by this example.

What I claim is:

1. A process for the manufacture of lead steel which comprises the steps of: melting a steel to which lead is to be added; and introducing a mixture of lead'and at least one rare earth metal into said molten steel.

2. The process according to claim 1, wherein said mixture is in a form selected from the group consisting of alloys, sintered aggregations and mixtures thereof.

3. The process according to claim 1, wherein said mix ture is introduced in a particulate solid state.

4. The process according to claim 1, wherein said mixture contains from 2% to 30% by weight of said rare earth metal, the balance being essentially lead.

5. The process according to claim 1, wherein said introducing step introduces said rare earth metal in a quantity of from 0.02% to 0.30% by weight of said molten steel.

6. The process according to claim 1, wherein said mirtture contains from 2% to 30% by weight of said rare earth metal, the balance being essentially lead; and in which said mixture is introduced into said molten steel in a quantity of from 0.10% to 0.80% by weight of said steel.

7. A steel containing conventional elements together with 0.10% to 0.80% lead and 0.02% to 0.30% of a rare earth metal, the balance consisting essentially of iron and said conventional elements.

8. A steel according to claim 7, wherein said conventional elements are selected from the group consisting of carbon, manganese, silicon and phosphorous, the total weight of all of the members of said group not exceeding about 1% of the weight of said steel.

9. A steel according to claim 7, wherein said lead constitutes 0.10% to 0.35%, and said rare earth metal constitutes from 0.02% to 0.08% by weight of said steel.

10. A steel according to claim 9, wherein said conven- 6 tional elements are selected from the group consisting of carbon, manganese, silicon and phosphorous, the total weight of all of the members of said group not exceeding about 1% of the weight of said steel.

References (Zited by the Examiner UNITED STATES PATENTS 2,182,758 12/1939 Harder 75--123 2,197,259 4/1940 Nead 75129 2,259,342 10/1941 Harder 75-129 2,811,720 10/1957 Fritts 75166 2,811,721 10/1957 Fritts 75l66 2,961,387 11/1960 Slatin 20464 3,016,436 1/1962 Latferty 75-152 3,152,889 10/ 1964 Holowaty 75123 3,203,788 8/1965 Contractor 75128 OTHER REFERENCES Zeitschrift fur Metallkunde, vol. 35, No. 6, February 1943. pp. 39-42.

DAVID L. RECK, Primary Examiner. P. WEIN STEIN, Examiner. 

7. A STEEL CONTAINING CONVENTIONAL ELEMENTS TOGETHER WITH 0.10% TO 0.80% LEAD AND 0.02% TO 0.30% OF A RARE EARTH METAL, THE BALANCE CONSISTING ESSENTIALLY OF IRON AND SAID CONVENTIONAL ELEMENTS. 